I'm also a Prime member but the main reason I go with them is to reduce risk. It reduces the risk that I will by a faulty product due to the reviews and return policy and it reduces the risk that I will drive to a store and be unable to buy what I originally came for which may necessitate another trip.

I also use Amazon for "groceries" just not fresh ones. In the past I've bought snacks, ramen, and peanuts from them.